Q&A: Polyurethane Adhesive Vs. Polyurethane Caulk

Three experts answer common questions about the sticky stuff

Q.What’s the
difference between polyurethane construction adhesive
and polyurethane caulk? In a pinch, can polyurethane
caulk be used as an adhesive?

A.In a pinch
— yes, but I wouldn’t make a
habit of it. While adhesives and caulks share the
same resin (polyurethane), they are formulated for
distinctly different purposes. In the case of wood,
glues form the best bonds when they penetrate and
wet the two parts, then cure to a hard, rigid
solid. On the other hand, caulks are expected to
"cling" to two surfaces (often of dissimilar
materials) as well as to bulk up and fill the gap
between them. This requires a less rigid and more
elastomeric substance, so the caulk is loaded with
fillers and additives that allow the caulk to move
when the joint is stressed, then return to its
original shape.